This patent application broadly relates to a sail intended to be used with a small to sailing craft, and more specifically to a radial sail for use with an unstaged, non-braced mast.
Modern sailing craft are typically equipped with a triangular-shaped main sail connected along its luff to a mast. A clew of the sail is attached to the aft end of a boom, the boom being held at its forward end to the mast. Many small sailing-craft, such as dinghies, sailboards, and Laser™ class sailboats have neither jib sails nor mast stays. The free-standing masts of these so-called cat-type rigs can therefore be subject to extreme forces. Even when initially setting the sail, the requisite preloading causes the mast to deflect considerably. Under way while sailing, the influence of the wind causes increases mast deflection, and the sail shape further changes unfavorably.
In order to keep undesirable sail deformation within acceptable limits, it has been one practice to use thicker masts with large cross-sections. But placing a thick mast along the leading edge of a sail affects aerodynamic efficiency quite unfavorably, not only by slowing down the air flow but also by creating turbulence, which in turn destroys suction on the leeward side of the sail. In order to avoid these disadvantages there has been a move towards using thinner masts, with the attendant disadvantage of more mast deflection and even possible mast failure.
By and large, sails are made by sewing together a number of cloth panels. Dacron, a trade name for polyester fibers manufactured by DuPont, is one popular is sailcloth material. However, other woven or laminated fibers or materials can often be used.
When it comes to sails built from panels of cloth, there are two basic types of construction: cross-cut and radial-cut. Cross-cut sails are ordinarily made from multiple overlapping fabric panels with the seams between each panel oriented in a fore and aft direction, parallel to each other and perpendicular to the leech. In most cases, the cross-cut panels are rectangular or almost rectangular in shape.
The fabric panels that make up radial-cut sails, on the other hand, are usually oriented toward the corners of the sail. This means that the seams between panels are not parallel, but rather radiate out from the corners of the sail. This results in panels that are triangular or nearly triangular in shape.
From the perspective of a sailmaker it is measurably more efficient to build cross-cut sails than to build radial-cut sails. With broad, almost rectangular cross-cut panels, there is less material waste than with the triangular-shaped panels needed for radial construction. Thus, cross-cut sails tend to be less expensive.
In particular, radial-cut panels must typically be oriented such that the direction to of highest stretching resistance extends in the same direction as the principal load lines of the sail. This manufacturing method entails significant waste and thus makes manufacture more costly. However, their strength and load-carrying ability mean that radial sails are generally thought to have superior performance over cross-cut sails.